The present inventions relate to the means for water treatment, preferably drinking water, and can be used in domestic water purification systems.
There is known a domestic reverse-osmosis system with a storage device for water that contains placed in the outer housing of the storage tank an elastic shell hermetically separating its cavity into two parts: the internal part changing cyclically its volume depending on the amount of purified water in it, and the outer part arranged between the shell and the housing of the storage tank, and also includes a control valve for water pumping into the outer chamber and control valve for water drain from the cavity to drainage.
In the prior art, there is known a number of U.S. patents (for example, U.S. Pat. Nos. 4,579,242; 4,585,554; 4,604,194; 4,629,568; 4,650,586; 4,705,625; 4,776,952; 4,885,085; 4,997,553; 5,662793, etc.) that describe water purification systems with storage devices for water including an air cavity.
At the same time, in water purification systems, there are used mechanical valves (for example, U.S. Pat. No. 4,997,553), piston type valves (for example, U.S. Pat. No. 3,887,463), and membrane type valves (for example, U.S. Pat. No. 4,190,537).
However, practical implementation of these devices is difficult since it requires a complex, highly reliable control system for water-to-water storage device.
There is known a water purification system using a device to accumulate purified filtered water, which is described in U.S. Pat. No. 6,764,595 published on 20 Jun. 2004, produced by Kinetico Incorporated, which is chosen as a prototype for the system and storage device.
The system includes a reverse-osmosis membrane, storage tank and control unit (block diagram shown in FIGS. 3A and 3B). The storage tank of the known water purification system is equipped with an elastic shell arranged inside an external vessel of the tank, which shell is intended for purified water (leachate or permeate), and a pumping area formed in the space between the shell and the vessel housing. In the system of water purification, the input of reverse-osmosis membrane is intended to supply pressurized tap water, and the output of reverse-osmosis membrane coupled with the shell cavity of the storage tank is connected with the tap for clean water via an outlet pipe.
Another output of reverse-osmosis membrane is connected with the drainage where the water with filtered impurities (concentrate) is discharged. For managing water pumping into the storage tank and discharge of the concentrate into the drainage, the system is equipped with two control valves connected in series, one after the other. That is, the system control unit includes a water-pressure-sensitive automatic primary control valve for water pumping (Pilot Valve), which valve has a controlling chamber and a controlled chamber, as well as a slave valve (Servo Valve) for drainage control with a controlling chamber and a controlled chamber. The controlling chamber of the Pilot Valve is connected with a tap of clean water via an outlet pipe, and the input of the controlled chamber is connected with the pipe-line. In the drainage control valve, the input of the controlled chamber is connected to a pumping water zone in the storage tank, and the output of the controlled chamber is connected to the drainage.
The described system uses combined type valves, which valves are driven by control pressure through the chamber containing an elastic membrane, and their shifting is performed using a piston spool.
The large number of inputs-outputs for the valve of control unit, i.e., large number of points needed in sealing, evidences a high degree of risk of potential leaks in the system, which reduces the reliability of the system. At the same time, a large number of connections in the system, as well as the connecting scheme, in which the control valve for water pumping is not coupled directly to the storage tank, but only through the drainage control valve, allows to make a conclusion on the complexity of the water purification system control unit, which reduces reliability of the system.
In addition, the storage device has the stagnant zone, which transfers hydraulic pressure, but in which the water does not circulate. In these areas, bacteria and germs develop, penetrate in time the line of clean water, and deteriorate its quality.
Storage tanks for water treatment systems include flexible membranes (shells, cells) designed to separate objects of storage and accumulate intermediate objects.
There is a group of tank constructions with a membrane that has reduced comparatively with the overall dimensions a connecting part—the neck. Such membrane configuration greatly simplifies connection to the tank housing and organization of stream redirection, allows to reduce sealing part dimensions and therefore tensions in sealing elements. Further, the configuration with the neck provides a possibility to remove the membrane sealing zone from the area of connection of tank housing elements, or to use one-piece tank housing.
Using the construction of storage tank with an elastic membrane in the system of water purification is known, for example, from aforesaid U.S. Pat. No. 6,764,595 of Kinetico Incorporated.
Traditionally, similar membranes are manufactured using different methods. One method is direct or transfer (flow) molding of rubber compounds with subsequent removal of vulcanized products from a punch through a narrowed neck. Some types of rubbers have feature of high relative elongation, and also the punch cross section has figured shape, which allows to carry out the process of removal without damaging the product. The disadvantages of this method are energy intensity and duration of the product vulcanization process, and also the high complexity of the removing operation. Another method for obtaining membranes is pressure molding thermoplastic elastomer with subsequent removing a cooled product from punch through the neck. However, smaller in comparison with rubbers relative elongation of thermoplastic elastomers significantly complicates removing a product and the construction of a punch. Besides, pressure molding technology, which substantially reduces the cycle time, limits the thickness of the casting walls, and makes it difficult to obtain a membrane with a thickness of baseline minimum to perform its functions.
As a prototype, selected is a storage unit for filtered water described in U.S. Pat. No. 4,997,553 of 5 Mar. 1991, which storage unit includes a housing (of a tank) with an elastic shell inside performed of thermostatic elastomer and fixed to the housing using the neck that isolates hermetically the inner cavity intended for storing clean water from the volume formed between housing walls and shell walls intended for discharging process water.
During the operation, the membrane body is cyclically compressed and extended changing divided volumes, while the neck remains firmly fixed in the tank providing a seal. This gives rise to different requirements on mechanical properties of different parts of the membrane: the membrane body shall be more durable, flexible and wear-resistant, while the neck shall be more rigid. The prototype does not solve the aforesaid problem.